Such devices may be of most different types and used for different types of signal transmission, both of numerical and analog character, said signals arriving to the bus of the device from, for example, a central unit or other devices as well as to the terminals from different electrical arrangements. The signals also travel in the opposite direction for bidirectional communication. A signal adapting module is then preferably arranged between the units for adapting signals. By way of example it may be mentioned that analog signals arriving to the bus of the device may be measuring signals from any pressure, temperature or flow sensor, and an analog output signal may then be sent to the terminals for controlling a regulator, for instance a valve regulating a flow, or a member regulating the temperature of an oven. The signals arriving to the bus of the device through the terminals may, in the numerical case, derive from contactors or similar electrical components, while the returning signals may control for example a motor through a contactor. The bus may also enable communication between different devices interconnected and a central unit. Furthermore, the device or the electrical arrangements connected thereto may receive their power supply through the bus. Devices of this type are fixedly interconnected, i.e. mechanically interconnected, through means, which in prior art devices resulted in considerable problems when any part of any device had to be repaired. In such a case the entire device had in the prior art devices to be separated from adjacent devices through disconnecting the means, thus breaking the continuity of the bus extending through the devices. This problem with known devices is schematically illustrated in FIGS. 1 and 2. Different devices 1' are connected to each other through co-operating assembling means 2', 3' at the respective device bus inlet 4' and bus outlet 5'. A series of devices 1' are in this way closely connected to each other side by side and preferably arranged on a mounting rail of a frame or the like. Such a device 1' comprises, as mentioned in the introduction, a bus unit as well as a terminal unit electrically connected thereto, which also are arranged as a continuous unit. These units may have an arbitrary content of signal adapting components and terminals. If a need of a replacement or repair of a device arises, a device having other devices on both sides thereof, as for example, the second device seen from the left in FIG. 1, the devices on both sides thereof are to be displaced to the left and to the right, respectively, as illustrated in FIG. 2, by a sufficient distance for creating such a gap that a separation of interconnecting means 2' and 3' of the buses may take place, and the device or the module may then be removed. This operation has to take place un the opposite order when a new device is to be inserted between other devices. This mode of changing devices when required is of course a drawback, since the very exchange is burdensome, requiring a displacement of the devices in one direction for creating a space for replacing a device. This means that in most cases a larger number of devices have to be displaced when one single device is to be exchanged, and such a displacement is troublesome since most of the devices carry terminations for cables to electrical arrangements. Furthermore, space has to be provided for such displacements of the devices, which means that they may not be arranged at such a high density as desired.
A considerable disadvantage of these prior art devices consists in the fact that entire devices have to be removed also if there is only a mechanical damage of any of the terminals thereof and this has to be repaired.